1. Field of the Invention
This invention relates generally to microprocessor based gaming systems used in gambling casinos, and more particularly to a method of authenticating game data sets in an electronic gaming system.
2. Brief Description of the Prior Art
Microprocessor based gaming systems are known which are used in gambling casinos to augment the traditional slot machine games (e.g. three reel single or multi-line games) and card games, such as poker and black jack. In a typical gaming system of this type, a microprocessor based system includes both hardware and software components to provide the game playing capabilities. The hardware components include a video display for displaying the game play, mechanical switches for enabling player selection of additional cards or game play choices, coin acceptors and detectors and the electronic components usually found in a microprocessor based system, such as random access memory (RAM), read only memory (ROM), a processor and one or more busses. The software components include the initialization software, credit and payout routines, the game image and rules data set, and a random number generator algorithm. In order to be acceptable for casino use, an electronic gaming system must provide both security and authentication for the software components. For this reason, gaming commissions have heretofore required that all software components of an electronic gaming system be stored in unalterable memory, which is typically an unalterable ROM. In addition, a copy of the contents of the ROM or a message digest of the contents (or both) are normally kept on file in a secure location designated by the gaming commission so that the contents of an individual ROM removed from a gaming machine can be verified against the custodial version.
In a typical arrangement, a message digest of the ROM contents is initially generated prior to the installation of the ROM in the machine by using a known algorithm usually referred to as a hash function. A hash function is a computation procedure that produces a fixed-size string of bits from a variable-size digital input. The fixed-sized string of bits is termed the hash value. If the hash function is difficult to invert--termed a one-way hash function--the hash function is also termed a message digest function, and the result is termed the message digest. The message digest is unique to any given variable size input data set, i.e., the game data set stored in the ROM. When it becomes necessary to later authenticate the ROM from any given machine, the ROM is physically removed from the game console and the message digest of the ROM contents is computed directly from the ROM using the original hash function. The computed message digest is compared with the message digest on file at the designated custodial location (typically in the casino itself). This procedure is typically carried out whenever a machine produces a payoff beyond a given threshold value. If the two message digests match, then the contents of the ROM are considered to be authenticated (verified) and the payout is made to the player.
While such electronic casino gaming systems have been found to be useful in promoting casino game play, the restriction requiring that the casino game program be stored in unalterable ROM memory, leads to a number of disadvantageous limitations. First, due to the limited capacity of the ROM storage media traditionally used to hold the program, the scope of game play available with such systems is severely limited. For sophisticated games using motion video and audio multi-media elements, much more memory capacity, on the order of hundreds of megabytes, is necessary. However, physical verification of such a large quantity of physical devices is not practical, and has thus far been an impediment to creating sophisticated games with more player appeal. Second, the authentication check is only conducted on a limited basis (usually after a jackpot) or other significant winning game outcome, and the authentication procedure requires that game play be halted until the ROM contents have been found to be authentic. These limitations make it very difficult to modify game parameters, such as the game rules or the payout scheme of the game being played on the gaming system. It would be advantageous to be able to modify the game parameters of a game currently being played on a game system without requiring physical verification of new games or game modifying data sets.